The specification of a mobile communication system using the CDMA (Code Division Multiple Access) method has been established as a mobile phone system of the third generation (IMT 2000), and the service has been started globally.
Characteristic functions of the mobile communication system using the CDMA method are a power control function and a handover function. By allowing these two functions to interact with each other, comfortable mobile communication environment (service) can be provided to the system subscribers, and carriers can accommodate more subscribers.
However, the mobile communication system using the CDMA method has a more complicated protocol, as compared with the mobile communication systems (TDMA (time-division multiplex access), FDMA (frequency division multiplex access), analog) of the second generation or before. Therefore, both the mobile terminal side and the base station side require the processing capability for a huge protocol. In order to solve this problem, progress in the semiconductor technique and the radio technique are essential. Accordingly, an increase in the circuit size and speed-up of the processing clock for improving the processing speed are required, and hence it is also necessary to improve the processing performance of the software for the protocol processing.
When services requiring real time, such as speech communication and videophone, are to be provided, it is necessary to minimize the transmission delay of data on the network.
As a factor contradicting the requirement for minimizing the transmission delay, there can be mentioned handover processing on the base station side. In the handover processing, the radio control base station compares user data including a transport block from the same mobile terminal received by a plurality of radio base stations (nodes B) by using a plurality of parameters indicating the radio state of the received user data, to select and combine optimum transport blocks from the received user data.
The radio control base station takes into consideration the possibility that there is a reception time difference between user data received from the same mobile terminal by the respective radio base stations, and stores the received respective user data and the parameters for the user data in a memory, to read it and perform processing afterwards. The processing, that is, comparison and branching processing in a plurality of stages are performed by using a software unit or a comparator, being a hardware unit. However, by such processing, a transmission delay may occur against the requirement for minimizing the transmission delay of the user data on the network.
FIG. 4 illustrates the overall configuration of a mobile communication system in which the method of obtaining user data to be transmitted to a network side is executed by selecting and combining user data including a transport block transmitted from the same mobile terminal.
As shown in FIG. 4, the mobile communication system comprises mobile terminals 1 carried by users, a plurality of radio base stations (nodes B) 2 which communicate with the mobile terminals 1, and a radio control base station (RNC) 3 which controls the plurality of radio base stations 2.
The radio control base station 3 comprises a user data reception processing section 31 for receiving user data including a transport block from the radio base station 2, and a selection and combination processing section 32 for selecting and combining user data transmitted from the same mobile terminal, which has been received via the radio base station 2, to obtain the user data to be transmitted to the network side.
The user data transmitted from the same mobile terminal 1 is received by a plurality of radio base stations 2. The user data transmitted from the same mobile terminal 1 and received by the respective radio base stations 2 is transmitted to the radio control base station 3, by using the Iub for communication protocol (Iub frame protocol). The radio control base station 3 selects and combines optimum transport blocks from these user data transmitted from the same mobile terminal 1, and transmits the combined user data to a core network (CN) side by using the Iu.
Conventionally, the radio control base station 3 uses a plurality of parameters in the Iub frame protocol to select a transport block included in the user data from the same mobile terminal 1, to obtain the user data to be transmitted.
The plurality of parameters in the Iub frame protocol includes parameters of the types described below. These parameters are based on TS25.427 in the 3GPP Standard.
(a) Header CRC
A parameter for deciding whether the header part of the Iub frame protocol is normal, that is, a parameter indicating the transmission condition in the network.
(b) Frame Type
A parameter indicating whether the Iub frame is a user data frame or a control frame.
(c) CFN (Connection Frame Number)
A connection frame number set between a mobile terminal and the radio base station, which is a parameter for indicating the frame order.
(d) TFI (Transport Format Indicator)
A parameter set at the time of call setting, and a parameter for deciding the type of user data transmitted from a mobile terminal. More specifically, it is a parameter indicating the number of the transport blocks and the size of the transport blocks.
(e) Transport Block
A parameter indicating the user data transmitted from a mobile terminal.
(f) Estimated Quality (QE)
A parameter indicating the bit error rate in the received data received by the radio base station.
(g) CRCI
A parameter indicating whether the CRC on the radio for each transport block, attached to the received data received from the mobile terminal by the radio base station, is normal.
When a plurality of branches exists (that is, when a plurality of radio base stations receive the user data from the same mobile terminal), user data having the same CFN has been the object of selection and combination.
FIG. 5 is a flowchart for explaining the conventional processing operation by the radio control base station, which selects and combines user data including a transport block transmitted from the same mobile terminal, by using the plurality of parameters.
At step X1, it is verified whether the header CRC of the Iub frame protocol is normal, with respect to the user data received by a plurality of branches (a plurality of radio base stations 2 having received the user data from the same mobile terminal 1). If the header CRC is not normal, control proceeds to step X14, to annul the frame. On the other hand, if the header CRC is normal, control proceeds to step X2.
At step X2, it is verified whether the frame type is a user data frame or a control frame. When the frame type is the control data frame, control proceeds to step X15, to perform terminal processing of the control frame, and remove the branch from the objects to be selected and combined. On the other hand, when the frame type is the user data frame, control proceeds to step X3, to temporarily store the respective transport blocks (TB) and the respective parameters in the Iub frame protocol in a buffer.
At step X4, CFN frames (frames in respective branches to be combined) of the same timing received from the same mobile terminal 1 is read from the buffer, and at step X5, a branch having the normal payload CRC is selected.
At step X6, it is verified whether there is a plurality of selected branches having the normal payload CRC. If there is only one branch having the normal payload CRC, control proceeds to step X21, to select the branch and obtain the user data to be transmitted, and the obtained user data is transmitted. On the other hand, if there is a plurality of branches having the normal payload CRC, control proceeds to step X7.
At step X7, it is determined whether the number and the size of the transport block in each branch are the same, by the TFI in the Iub frame protocol. If not, control proceeds to step X16, and if yes, control proceeds to step X8.
At step X8, it is verified whether the number of branches in which the CRCI is OK is plural or single for each transport block. If there is only one branch in which the CRCI is OK, control proceeds to step X13, to select the branch to obtain the user data to be transmitted, and the obtained user data is transmitted. On the other hand, if there is a plurality of branches in which the CRCI is OK, control proceeds to step X10.
At step X10, it is verified in each branch whether the bit error rate (QE) is the same. If not, control proceeds to step X12, to select a branch having a lower bit error rate, and control proceeds to step X13. On the other hand, if the bit error rate is the same, control proceeds to step X1, to select a branch optionally, and control proceeds to step X13.
At step X13, the transport blocks of the selected branches are combined, to obtain user data to be transmitted to the network side having a switching system, and the obtained user data is transmitted to finish the processing.
At step X16, to which control proceeds when the number and the size of the user data in each branch is not the same, all transport blocks in the branches where the first CRCI in each branch is OK are selected.
At step X17, it is verified whether the number of branches in which the first CRCI is OK is plural. If there is only one branch in which the first CRCI is OK, control proceeds to step X21, to select the branch to obtain the user data to be transmitted, and the obtained user data is transmitted. On the other hand, if there is a plurality of branches in which the first CRCI is OK, control proceeds to step X18.
At step X18, it is verified whether the bit error rate (QE) in each branch in which the first CRCI is OK is the same. If not, control proceeds to step X20, to select a branch having a lower bit error rate, and control proceeds to step X21, to select the branch to obtain the user data to be transmitted, and the obtained user data is transmitted. On the other hand, if the bit error rate is the same in each branch, control proceeds to step X19, to select a branch optionally to obtain the user data to be transmitted, and the obtained user data is transmitted.
As described above, the conventional processing performed by the radio control base station in order to obtain the user data to be transmitted to the network side, in which optimum transport blocks are selected and combined from user data including transport blocks transmitted from the same mobile terminal, is complicated processing, wherein there are lots of comparison processing steps, thereby causing a transmission delay.